A planetary gear box can comprise a first outer (external) gear secured to an input shaft, a plurality of second external or outer gears meshing with the first outer gear, a plurality of crankpins which are connected to the second outer gears so that the rotary movement of the second outer gears is transduced into a rotational movement of the crankpins, and at least two geared wheels, or planets, which have a plurality of pin holes formed therein, which are circumferentially spaced from each other and outer gear teeth formed at the periphery of each planet.
The crankpins are inserted into the pin holes so that the eccentric revolutional movements of the planets, which are angularly spaced, are generated by means of the rotational movement of the crankpins.
An outer gear ring surrounds the outer gear teeth of the planets and has inner (internal) gear teeth which mesh with the planets, this gear ring being on or forming the outer part of the housing of the gear box either as a stationary or as a low speed rotating element. The crankpins are journaled in a planet carrier which is either the low speed rotating element or the stationary element of the planetary gear transmission.
Planetary gear boxes which have the construction mentioned above are described in U.S. Pat. No. 3,129,611 of Apr. 21, 1964.
However the planetary gear box disclosed in the above mentioned U.S. Pat. No. 3,129,611 does not satisfy all requirements for:
(a) a good power split of the input power between the different crankpins;
(b) a maximum reduction of the reaction forces of the meshing forces on the crankpin bearings; and
(c) the best possible realistic calculation of the effect of teeth load reaction upon the different crankpin bearings.
Each planet being a rigid plate, the different crankpin bearings of the same planet are in the same plane of a rigid plate. For this reason the meshing force acting in the common plane of the different crankpin bearings has completely different reactions on the different crankpin bearings, depending on the different clearances, due to machining tolerances, in the different crankpin bearings.
The variations in the reaction forces acting on the three individual crankpin bearings have a big influence for the power split between the different crankpins. As a result all the power of the input pinion could be transmitted by only one of the different crankpins. To avoid such a poor operating condition, the machining tolerances for all parts and particularly for the radial bearing clearances have to be extremely accurate for a construction as shown in U.S. Pat. No. 3,129,611.
On top of this, this planetary gear box has, as it is described, a large number of parts requiring very high precision machining to work properly. This is not economical.
Another planetary gear box which has the construction mentioned above is the U.S. Pat. No. 4,407,170 of Oct. 4, 1983, it has the same disadvantages concerning internal power split and bearings loads as U.S. Pat. No. 3,129,611, its planet carrier is different, it needs planet carrier bearings which are almost as large in diameter as the toothed part of the planets, this can be very expensive for industrial gear boxes where the planets have diameters.